The present invention is directed, in general, to telecommunication systems and, more specifically, to a method for monolithic integration of multiple devices on an optoelectronic substrate, and a method of manufacturing an optical fiber communications system associated therewith.
Optical fibers are key components in modern telecommunications and have gained wide acceptance. As is well known, telecommunication optical fibers are thin strands of glass capable of transmitting an optical signal containing a large amount of information over long distances with very low loss. Single fibers can carry multiple packets of data that are multiplexed on the fiber either by time division, where different slots of time are allocated to different packets, or by wave division multiplexing, where different wavelengths are allocated for different data. Optoelectronic devices, such as modulators and switches, perform the important function of adding information content to optical signals in optical communications systems. Such devices may include expitaxially grown multi quantum well type structures of an indium phosphide or indium gallium arsenide phosphide (InGaAsP) base. The quantum well type structures may be undoped, or may be doped with various n-type and p-type dopants.
Traditionally, the optoelectronic industry focused on hybrid integration of optoelectronic devices, wherein many optoelectronic devices are manufactured on individual optoelectronic substrates, all of which are subsequently connected by optical fibers. Hybrid integration was sufficient for traditional telecommunication devices, however, with the current increased demand for reliably carrying increased amounts of data, hybrid integration is problematic. Specifically, hybrid integration may experience poor optical coupling between the optical devices and the optical fiber, poor mechanical stability of the circuit, high cost, and low performance. Thus, in an attempt to circumvent some of the problems associated with hybrid integration, the current trend in the optoelectronic industry is to manufacture multiple optical devices on a single optical substrate. Manufacturing multiple optical devices on a single optical substrate, or so-called monolithic integration, is the ultimate solution to the problems discussed above, however, current manufacturing techniques each have problems associated therewith.
One manufacturing technique currently used to monolithically integrate multiple devices on a single optical substrate is called the xe2x80x9cbutt jointxe2x80x9d technique. The xe2x80x9cbutt jointxe2x80x9d technique typically consists of growing a first device structure, for example a laser, on the whole wafer, followed by selective etching and regrowth of an area not protected by a mask layer, and representing a second device. The xe2x80x9cbutt jointxe2x80x9d technique currently allows for independent design of different devices and is used by many manufacturers, however, it commonly experiences certain problems at the junction between the first device and the second device. For example, the xe2x80x9cbutt jointxe2x80x9d technique may experience edge effect issues at the junction, material quality issues at the junction, and dislocations at the junction that may produce optical losses by absorption.
Another technique commonly used to monolithically integrate multiple devices on a single optical substrate is a selective epitaxy technique (selective area growth). The selective epitaxy technique is based on variations in the band gap of multi quantum well materials in the same plane with a single growth step over a masked substrate. Grown material, which does not nucleate on the dielectric masked area is deposited nearby, inducing a local increase in growth rate. Epitaxial layer bandgap energy shifts may then be controlled by the geometry of the dielectric pattern. The selective epitaxy technique has certain benefits, however, it may only be used when two devices require the same number and composition of quantum wells. Moreover, without encountering problems with the material composition, the change in wavelength attainable by the selective epitaxy technique only ranges from about 50 nm to about 100 nm. Furthermore, the selective epitaxy technique may only be conducted with a metalorganic chemical vapor deposition (MOCVD) device, which may not be used in a majority of manufacturing plants, and is extremely expensive.
Another technique currently used to monolithically integrate multiple devices on a single optical substrate is a quantum well intermixing technique. Quantum well intermixing generally requires deposition of a selective mask over areas where the second device is desired, followed by a high temperature anneal in the presence of phosphorous or arsenic. The high temperature anneal causes a selective interdiffusion between the quantum wells and barriers below the selective mask, causing a shift in wavelength in the areas where the selective mask is located. The problem with the quantum well intermixing technique is that the high temperature anneal occurs at a temperature above the quantum well temperature growth rate, thus leading to degradation of the material quality. Moreover, the quantum well intermixing technique is limited to no more than two devices.
Accordingly, what is needed in the art is a method to monolithically integrate multiple optical devices on a single optical substrate, and a method of manufacturing a telecommunication system, which does not experience the difficulties and problems associated with the prior art methods.
To address the above-discussed deficiencies of the prior art, the present invention provides a method for monolithic integration of multiple devices on an optoelectronic substrate. The method, in a preferred embodiment, includes forming an active layer having a given wavelength over a substrate. The method further includes forming an N-type doped layer over a portion of the active layer to form first and second active regions within the active layer, the first active region having the given wavelength and the second active region having an altered wavelength different from the given wavelength. In one exemplary embodiment, the conditions used to form the N-type doped layer, for example, dopant concentration, growth rate and temperature, may vary the amount of difference in wavelength between the given wavelength and the altered wavelength. Because the N-type doped layer may be formed at temperatures at or below the temperature required to form the active region, degradation of the active region and diffusion of dopants therein are substantially eliminated.
The foregoing has outlined, rather broadly, preferred and alternative features of the present invention so that those skilled in the art may better understand the detailed description of the invention that follows. Additional features of the invention will be described hereinafter that form the subject of the claims of the invention. Those skilled in the art should appreciate that they can readily use the disclosed conception and specific embodiment as a basis for designing or modifying other structures for carrying out the same purposes of the present invention. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the invention in its broadest form.